This invention is generally directed to new toner compositions, and developer compositions containing certain charge enhancing additives. More specifically, the present invention is directed to developer compositions containing toner particles, and ortho-halo phenyl carboxylic acids as charge enhancing additives, which additives impart a negative charge to the toner resin particles. Developer compositions containing such charge enhancing additives are useful for causing the development of electrostatic latent images, including color images. Furthermore, the developer compositions of the present invention can be employed with common carrier particles of the same composition as compared to some prior art developer compositions wherein carrier particles of different compositions are needed, when such compositions are used to develop color electrostatic images.
Developer compositions containing charge enhancing additives are known in the prior art, particularly, those developers containing charge enhancing additives which impart a positive charge to the toner resin. However, very few developing compositions are known in the art wherein charge enhancing additives are emplofyed for the purpose of imparting a negative charge to the toner resin. Examples of positively charged toner compositions include those described in U.S. Pat. No. 3,893,935, wherein there is disclosed the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. This patent states that certain quaternary ammonium compounds when incorporated into toner materials were found to provide a toner composition which exhibited a relatively high uniform and stable net toner charge when mixed with a suitable carrier particle. A similar teaching is described in U.S. Pat. No. 4,079,014 with the exception that a different charge control additive is employed, namely, a diazo compound. Other charge enhancing additives are described, for example, in U.S. Pat. No. 4,298,672, wherein there is disclosed developer compositions containing as charge enhancing additives certain alkyl pyridinium halides, particularly cetyl pyridinium chloride for the purpose of imparting a positive charge to the toner resin.
In some instances, it may be desirable in electrostatographic imaging systems to produce a reverse copy of the original. Thus, for example, it may be desired to produce a negative copy from a positive original or positive copy from a negative original. This is generally referred to in the art as image reversal, which in electrostatic printing systems can be accomplished by applying to the image a developer powder which is repelled by the charged areas of the image, and adheres to the discharged areas. More specifically, for example, toner particles possessing positive charges are found to be very useful and effective in electrostatographic reversal systems, and in particular in xerographic systems employing organic photoreceptors, which in many instances are charged negatively rather than positively, thus necessitating the need for positively charged toner compositions.
In contrast, the present invention is concerned with negatively charged toner particles, that is, where the toner particles possess a negative charge rather than a positive charge, the negative charge being imparted by the charge enhancing additives of the present invention to be described hereinafter. Further, the charge enhancing additives of the present invention possess other desirable properties in that, for example, they are capable of imparting substantially similar triboelectric charges to all toner compositions irrespective of color. Also the toner compositions of the present invention can be incorporated into developer compositions containing common carrier particles.